A detailed investigation of induced residual stresses in the laser powder bed fusion process using the modified inherent strain approach and experimental measurements

In this work, a multiscale finite element model is proposed to simulate the Laser Powder Bed Fusion (LPBF) process, employing the Modified Inherent Strain (MIS) methodology. MIS is a more sophisticated approach than the conventional Inherent Strain (IS) technique, initially developed for welding process simulations. Due to the complex thermo-mechanical interactions present in the metal Additive Manufacturing (AM) process, the MIS approach has evolved to account for these interactions, in which sequentially deposited layers act as mechanical constraints on earlier layers, influencing stress and strain evolution throughout the process. A multiscale modeling approach can effectively predict the residual stresses induced during LPBF, which are essential for assessing the quality and performance of the manufactured part. This study provides a novel contribution by systematically validating MIS-based residual stress predictions against depth-resolved X-Ray Diffraction (XRD) measurements up to 3 mm below the surface, addressing a critical gap in the literature where prior works primarily focused on surface-level stress or distortion. Laser power and scanning speed, which are critical process parameters, were modified to investigate their individual impacts on the residual stress distribution in the longitudinal and transverse directions. Simulated results were validated through experimental XRD measurements on fabricated Inconel 625 test coupons. While the MIS method aligns well with the experimental data at the surface level, discrepancies arise in deeper subsurface layers, where simulations tend to underestimate tensile residual stresses due to simplified MIS assumptions. Refinement, such as improved thermo-mechanical coupling and adaptive heat source models, may enhance stress prediction accuracy in the LPBF process. By offering a comprehensive depth-resolved analysis, this work provides new insights into subsurface stress evolution, critical for ensuring the structural integrity of LPBF parts. The study provides a critical assessment of the MIS method's capabilities and offers essential guidance for future research opportunities to improve residual stress predictions in LPBF-produced parts.